Q&A Notes on Interview from World Construction Forum
Prof. Eng. Toshimi Kabeyasawa
Earthquake Research Institute, The University of Tokyo
Sep 13, 2018
We all know that Japan is located in the region with high natural hazards and that it has a lot of experience in reactions to extreme natural events, which can be used to enhance resilience to natural hazards in a future. There are probably several different Committees which deals with this issue. In last 3 years you served as a Head of Disaster Investigation Committee. Can you please explain how important is the knowledge which is obtained by studying the effects of earthquakes on buildings hit by severe earthquakes?
Resilience of a society to natural hazards have been mainly enhanced by historical experiences and knowledge. Earthquake and any other natural disasters have occurred repeatedly and worldwide but very rare in a region compared to human life span, so that historical experiences and knowledge on them are apparently inevitable for proper and rational countermeasures to mitigate or prevent probable disasters in the future. Historical records, engineering solutions and scientific understandings should be sheared through regions and generations because the events are very rare compared to human life span. Earthquake engineering backgrounds, such as seismic design and practices for structures, have been rapidly developed in these sixty years, with observations, theory, experiments and numerical simulations so on. However, deign methods and criteria are still based on damage experiences and lessons from past disasters of far more years from starting constructions before sophisticated modelling and calculations had become available. There could be excellent performance in the traditional systems which have not yet identified by modern numerical simulations. On the other hands, we might still have overlooked some critical behaviours in design analysis or code specifications so on. These rare phenomena might possibly appear and be awaken at the time of very rare events, such as on lack of proper details in real construction practice, insufficient design modellings and calculations for actual buildings. Proper field survey, precise records, and data analysis at these rare events may be compared as variable as huge scale experiments, which have not yet been executable artificially in the laboratories. Numerical simulations could be another tool, though still need be verified further especially on the accuracy of the assumptions and modellings.
In Europe, the quality of buildings in terms of safety is very versatile. Especially existing buildings can be extremely vulnerable. On the other hand, society, at least in Europe, is often not aware about the fact that some existing buildings are not safe. In such cases at least the regulator should be more responsible and react, especially in the case of ensuring safety for future generations, children. I have in mind the safety of schools. How Japan is solving this issue?
Countermeasures for future generations are primarily important. Retrofit of schools has been one of the priority targets in Japan after the experience of 1995 Kobe earthquake. Japanese government enact a law for promotion of seismic retrofit, which makes seismic evaluation and retrofit mandatory for the selected important buildings, such as schools, public halls, government offices, power stations, hospitals and large stores, for public use. Public school buildings and gyms have been used temporarily as local evacuation centers after recent earthquakes. The retrofit design and strengthening are obligatory in existing buildings also when the large-scale renovation is under planning, as such large as official permission is required. The seismic performance evaluation and systematic retrofit of public schools have been performed after 1995 as a political measure with financial aids from national government to local governments, i.e., public school owners, and even to private schools also. The retrofit of public schools has been almost completed Japan wide, for example, 96.2% in 2013, and 100% in Kumamoto city at the time of 2016 Kumamoto earthquake as shown in the statistics below by the Ministry of education. This is also the case mostly for the important public infra-structures, such as bridges, express way, power stations, so on.
The construction of new buildings as well as retrofit of existing structures is regulated by standards for earthquake-resistant designs. You have great experience in the he filed of reinforced concrete buildings. Can you please briefly describe current situations of buildings codes in Japan? What are plans for future?
Two levels of seismic design objectives and criteria are basically specified accordingly with two phases of seismic design procedures. Several ways of seismic design analyses are available for practical calculations such as from simple specifications to time-history response analyses according to size, height, structural types of buildings and so on. The design regulations in Building Standard Law have been basically preserved after the revision in 1981, though partial amendments have been made several times after damage experiences by recent earthquakes so on.
The performance objective of the first phase design is to control damages under moderate/rare earthquake motions. Elastic analysis is used under static loadings with standard base shear coefficient of 0.2 for verifying allowable stress design criteria in a typical practical design procedure, partially using ultimate member strengths. The second phase performance objective is to ensure safety under severe/very rare earthquake motions. The safety performance was verified through limit analysis in the early stage while pushover analyses is being used mostly in these days based on inelastic characteristics of members. The required seismic capacity is specified in accordance with the inelastic deformation capacities of moment-resisting frame members and walls specified with graded parameters of members. The base shear coefficients required for reinforced concrete buildings are specified from 0.30 to 0.55 by step size of 0.05, based on the ratios of earthquake loads carried by the frames and the walls graded with deformation capacities. The objective ultimate capacities are increased for irregular structures. Seismic zone factors have also been introduced considering historical seismicity, though most of recent severe earthquakes have been occurring in the zones with reduced factors, such as Kobe, Niigata, Kumamoto and Sapporo, mostly induced by inland active faults with relatively long return periods.
There was a chance to move on to performance-based seismic design or displacement design using inelastic response estimation and calculated deformability at the time of revision of Building Standard Law in 2001. The method is regulated and nearly ready for practical use. However, a huge scandal with fake structural calculation hit the administration in 2005, so that the specification and review process were made very strict including the computer codes. In the reforming process, the large difference between the traditional calculation and the new performance-based calculation was pointed out so that the Ministry of construction had to make the performance-based design unavailable practically for the time being. Actually, there were still left in practical procedures of PBD to be sophisticated or investigated so as to be applied for all types of buildings. Even after seismic calculation has been enough sophisticated in PBD, engineering judgement and considerations would still be important for disaster preventions, because there might be left still unknown assumptions, especially on the design earthquake intensity in the future. Therefore, the design procedure and simulation would better be simple and transparent to reflect the engineering considerations of designers. Also, a fail-safe concept would be much important in the standard design procedure.
Japan is world-leading country in performing experiments on shaking table using full-scale specimens. The shaking table E-defense can be used to investigate seismic performance of multi-storey reinforced concrete buildings. How important are such experiments to improve construction in future? Can you tell as more about these latest experiments which you plan to perform?
A full-scale six-story building was tested at E-Defense in 2006, which was first full-scale dynamic test under 3-D motions. There have been several tests in a year, so it makes several tens on various types of structures with various objectives from 2006 to 2018. I have several chances to be involved in some of the tests. However, I can not think of typical examples, which had affected design codes/regulations or new construction systems directly and explicitly with such verified results. Background reasons are not detailed here.
However, positive responses have been often been heard from leading structural engineers and practitioners around that they could be much more confident in traditional ways of design and construction, by observing the actual response behaviour of the building specimens on the table, even in particular cases. Also, they could recognise that the difference between design calculation and actual responses are not negligible, even in structural capacity based on flexural strengths of members. They could follow the real time responses again and again through the videos also with the measured test data, which were different from the experience of post-earthquake damage survey on site. The shake-table tests could be efficient tools for training practitioners as a result. This is also the case for the development of design analytical models by researchers or code makers. The VTR can be downloaded from the web of NIED, or more by DVD and some of test data by direct contact to NIED.
The next test in our interest is to be conducted in Dec-2018 to Jan-2019, as the second full-scale ten-story building with sliding/fixed bases. Observers are expected not only from Japan wide but also from worldwide registered in advance with due process through HP of NIED.
Japan is very frequently hit by extreme natural events which cause a lot of losses of human lives, injures and homeless people, as well as huge economic loss. It often occurs that one extreme event (e.g. earthquake) causes a chain of events (e.g. tsunami, flood, landslide, fire). Can you please comment how Japan is planning to further enhanced the resilience to natural hazards?
“Disaster comes when passing from our remembrance”
An aphorism based on speech by Dr. Torahiko Terada, who founded Earthquake Research Institute, University of Tokyo, in 1925, – the concept is shared with most of elder Japanese.
“Harmony should be valued (and quarrels should be avoided).”
The first sentence in The Seventeen-Article Constitution established by a Japanese Emperor in 604.
Harmony-oriented spirit or community-oriented mind are found not only in Japan but also worldwide more or less. They seem to be disappearing in large cities during recent decades, though they are still preserved especially in local areas of Japan. The community-oriented mind seems to have been bred traditionally through cooperative works within community such as for not only rice production or fishery but also public works for maintenance of land/forest as well as countermeasures against frequent disasters. Gardens at castle, shrine and temples were used for evacuation places after natural disasters, and preserved foods were sheared. They have traditions of systematic mutual assistance among community members. Also, national land conservation has been one of the main political issues of the governors, such as flood control measures and tree plantation.
After WWII, LDP, i.e., the liberal democratic party, conservative, has been ruling party long time in Japan, for which contractors union is one of major supporters, which means national land conservation has been one of the main political issues Japan wide. However, a few years before the East Japan earthquake 2011, Democratic party, , innovative or mixed left wings, took control of national government instead whose slogan was “concrete to human.” They had cut down the budget for public works radically, even on continuing project for many years. The contractors had sold construction machines to overseas and reduced new employment for the years. Then the East Japan earthquake occurred and the new government responses to the disaster were terribly inconsistent and poor. We are now still in after-trouble by the one-sided law at that time, e.g., on electric power supply. All NPPs still have to stop generation due to high level of restrictions, while huge areas of forests and fields are being destroyed by solar panels, treated by unfair law, some of which are invested by foreign capitals. Trade deficit for several years after 2011 was apparently due to the increase of oil import for electric power supply, which has still been subject to accidental black out due to inadequate capacity, such as occurred in Hokkaido, 2019.
Now back to put LDP into power, economic recovered well by money supply and investment on infra-facilities, land and constructions as well as disaster preventions became much active again. I am supposing that Japanese people well understand traditionally or historically the importance of continuing and cooperative efforts on national land preservation, which results in defense against future natural disasters. It was not much popular in the past election to emphasize disaster defense policy so on though it seems to be much more conscious after recent experiences of more frequent and unusual natural disasters such as floods, global warming, earthquakes, and volcano eruptions.
(However, I am afraid we are still too less conscious or brainwashed about national defense with sovereignty right against neighbourhood countries after the experience of World War II and the occupation policy by USA(WGIP). This is another story.)